Environmental and economic analysis of Landfill biomining process in the context of utilizing rdf as fuel and good earth as subgrade material for flexible paved road: a life cycle and cost-benefit approach

Abstract

Landfills of municipal solid wastes in India create significant environmental and socioeconomic issues due to inadequate maintenance. To address these impacts, Solid Waste Management Rule, 2016 proposes 'Landfill Biomining' as a viable solution. Two landfill sites, Howrah and Durgapur, are examined in this study using Life Cycle Assessment (LCA) and Cost-Benefit Analysis (CBA) models to evaluate the environment and economic performances of this approach by utilising different products of biomining. Four scenarios are considered: the base scenario (Do Nothing Scenario), where biomining occurs but the products are utilized for in-situ filling or covering purpose; Scenario 1, which involves using refuse-derived fuel (RDF) to replace coal in cement factories or brick kilns; Scenario 2, which uses good earth as subgrade material in roads; and a combined scenario incorporating both Scenario 1 and Scenario 2. The environmental analysis reveals that these mining and waste valorization strategies can significantly reduce the global warming potential of landfill waste. In the combined scenario, where RDF is used in cement factories or brick kilns, each site can replace an average of 208 kg of coal by the RDF obtained per ton of legacy waste. This results in a substantial reduction in Global Warming Potential (GWP), with the Durgapur site achieving a 53.92% reduction and the Howrah site achieving a 55.58% reduction. The feasibility of using the good earth as subgrade material has been evaluated through physicochemical, geotechnical, and heavy metals analysis. The results, compared with the literature values and regulatory guidelines, indicate that good earth obtained from both Howrah and Durgapur sites are suitable for subgrade material. Specifically, Howrah’s unsoaked California Bearing Ratio (CBR) is 14.18%, while Durgapur’s is slightly higher as 15.22%, suggesting marginally better loadbearing capacity in dry conditions. However, good earth of Howrah site has higher heavy metal concentrations compared to Durgapur. Economic performance has been assessed through a Cost-benefit analysis model, which would include the Net Present Value (NPV) and Costbenefit Ratio, considering direct costs, indirect costs and carbon emission reduction (CER) credits obtained from LandGEM gas emission model as environmental benefit. The NPV analysis has shown positive net benefits for both landfills, with Howrah and Durgapur sites yielding 6,93,22,572.45 INR and 37,25,64,154.68 INR, respectively considering the RDF is utilised in cement factory as replacement of coal and good earth is used as subgrade material of road. The Cost-benefit analysis has identified transportation and coal replacement costs as the major factors influencing economic viability. Although the environmental and economic performances of biomining of landfill is case specific, the results of this study can be used as a benchmark for the feasibility analysis of future biomining projects considering circular economy and environmental sustainability.